Last time I graded a batch of undergraduate papers for a big lecture class, I spent more time online searching for the sources of peculiar phrases than I did correcting grammar or engaging ideas. Why would anyone (other than a bookish pirate) call a character from The Grapes of Wrath a “saucy wench”? Ask the good folk at http://www.sparknotes.com, from whence this lazy sophomore had lifted most of his paper. I printed out the source, made a copy of his paper and sent the whole package off to a dean’s office charged with handling violations of academic integrity.

I told the student I couldn’t return his paper because it looked to me as if he’d copied it off the Web. “You get an F,” I said. He shrugged. But before the dean got around to his case, he turned in a second paper. This one seemed pretty good, until I found an identical paper deep down in the pile. He’d gotten a little trickier: I couldn’t trace this one with a simple Google search; to find it, I had to subscribe to an advanced SparkNotes service. The whole episode was depressing.

The students who cheat-particularly off the Web-seem to be missing the gene that provides a moral compass on issues of intellectual property. Or maybe there is no such gene and they simply missed the day in elementary school when the overworked teacher reminded the kids to make a note of where they find the information they download off the classroom computer.

It’s harder to excuse the group of cheating or maybe careless grown-ups whose stories inspired Peter Charles Hoffer’s compelling Past Imperfect: Facts, Fictions, Fraud-American History from Bancroft and Parkman to Ambrose, Bellesiles, Ellis, and Goodwin. A professor of history at the University of Georgia, Mr. Hoffer is the former chair of the now-disbanded Professional Division of the American Historical Association. Past Imperfect is a brief for the Professional Division, whose task was to determine whether an individual historian, charged with malfeasance-plagiarism or faking data-actually violated the association’s Statement on Standards of Professional Conduct.

Mr. Hoffer works through the details of these four famous cases from the last decade. Stephen Ambrose, author of best-selling books on Lewis and Clark, the transcontinental railroad and D-Day, had a habit of building gripping narratives by lifting firsthand accounts from books by other writers. To readers, it seemed as though the remarkably productive Ambrose had found all the primary sources he used, and he often cited them without properly acknowledging the writers who had discovered them in the archives. The charge may seem fastidious, but it was wrong for Ambrose to present as his own the words of other scholars. It must have been disheartening for them to watch Ambrose grow rich and famous using their work.

Ambrose misappropriated sources; Michael Bellesiles apparently made his up. Mr. Bellesiles was a professor at Emory when his book Arming America: The Origins of a National Gun Culture was published by Knopf in 2000. He must have known that the National Rifle Association would not much like his contention that gun ownership was rare in early America and that the Second Amendment was meant to apply to militias and not to individual citizens. The book won praise in the press and prizes from the profession. But Mr. Bellesiles was very careless about the probate records that supposedly supported his case and less than forthcoming with the committees from his university set up to investigate the charges against him. Had he visited the archives? Did the records he said he’d used exist? Were his notes destroyed by a flood? Though Mr. Bellesiles lost his job, his book is still in print.

Doris Kearns Goodwin, biographer of the Fitzgerald and Kennedy families, Lyndon Johnson, and Eleanor and Franklin, was careless too in her use of sources. Her publisher paid off one of the writers whose work she copied, but at least Ms. Goodwin has been somewhat more candid than the others about her mistakes.

Mount Holyoke professor Joseph Ellis’ case is the strangest of the four. Mr. Ellis lied to his students about scoring touchdowns, leading platoons in Vietnam and fighting for civil rights in the South. He was a busy man in the 1960’s, when he was also in graduate school at Yale and teaching at West Point. His defenders said that at least he didn’t lie in his books or lie to advance his career. Mr. Hoffer, however, uncovers subtle patterns of invention that he thinks changed the way Mr. Ellis wrote his histories. The “bravado that Ellis injected into his fabrications went into his later books … made them different, and better, than his earlier efforts.” The more he lied to his students, the more artful his history became. In the end, all his college could do was to take away his endowed chair and force him to take a leave from teaching.

There’s plenty here to inspire the amateur analyst, but Mr. Hoffer is not interested in individual pathologies or even in the individual moral failings of these writers. Their cheating ways go right to the ailing heart of the history profession, which, to its detriment, has dropped the ball on governance. There’s something very wrong in the house of history when the right-wing Weekly Standard passes as the profession’s whistleblower and chortles over careless mistakes by liberal historians.

History matters to Mr. Hoffer because it tells us who we are as a people and a nation. Our views of the past shape the way we make policies and elect Presidents. In the first years of the Republic, the revolutionary generation took a deep interest in the history of the experiment that was the United States. History was to pull a people together into a sort of national consensus. Little matter that Indians, women, slaves and servants had no place in the national story; the tales of heroic New Englanders would stand for the experience of all.

We have changed this history, of course, but Mr. Hoffer suggests that our inclusive, contentious, diverse and self-critical history has come at a cost. Professional historians have lost a battle in the culture wars. Mr. Hoffer’s case studies expose an enormous gap between the critical histories we write for our graduate students and colleagues and the appealing popular narratives that sell well and turn historians into celebrities. These four fell into the gap and bartered their historians’ souls for money and fame. The lucky ones, like Ambrose, landed in a marketplace where the profession has no power even to shame.

It’s hard to say what Mr. Hoffer’s fine efforts can accomplish in that marketplace. Joseph Ellis’ new biography of George Washington sits in stacks at my local bookstore, piled up between other bestsellers-Jon Stewart’s America (the Book) and The South Beach Diet-and maybe not too far from books by the two newest members of the plagiarizing fraternity, Harvard’s Charles J. Ogletree Jr. and Laurence Tribe. I really don’t want to buy Mr. Ellis’ book. Why should I boost his profit on the work he did during his term of academic exile? But Peter Charles Hoffer’s Past Imperfect sets up a drama I can’t resist-the lying historian meets the President who could not tell a lie. Is this Mr. Ellis’ act of contrition? Will his famous imagination finally falter in front of an honest man? Or will this solid Founding Father crack into the mysteries of which Mr. Ellis is so fond? I’ve just sent my daughter out to pick up a copy.

Ann Fabian teaches American history and American studies at Rutgers University.